1. Field of the Invention
The present invention relates to an electrooptical apparatus having a function causing a part of a display screen to be in a display state and causing the other to be in a non-display state and a driving method therefor. Furthermore, the invention, using a liquid crystal display apparatus as the electrooptical apparatus, relates to the driving method for the liquid crystal display apparatus, which allows a partial display state without providing an incompatibility and with less power consumption, and it also relates to the liquid crystal display apparatus performing display operation according to the above. The present invention also relates to a driving circuit suitable for driving the electrooptical apparatus of the invention.
Furthermore, this invention relates to an electronic equipment to be used for the electrooptical apparatus and the display apparatus described above.
2. Description of Related Art
With display apparatuses being used for portable electronic equipments such as portable telephones, the number of display dots is increasing year by year so that increasing amounts of information can be displayed. Accordingly, power consumption by the display apparatus is also increasing. Generally, the portable type electronic equipment uses battery as a power source; therefore, reduced power consumption with the display apparatus is strongly demanded so that battery service life can be extended. That is why, a study has begun for development such that with a display apparatus having a larger number of the display dots, a full screen is displayed when it is necessary; however, in normal use, only a partial region of a display panel is allowed to be in a display state and the other is left in a non-display state so that power consumption can be reduced. Furthermore, in response to the demand for power-consumption reduction, as display apparatuses of portable type electronic equipment, liquid crystal display panels of a reflective type or a transflective type designed by placing importance on appearance in a reflection mode is used.
In conventional liquid crystal display apparatuses, they have, in most cases, a function allowing control of display/non-display operations on a full-screen basis; however, a display apparatus having a function that allows only part of a full screen to be in a display state and allows the other to be in a non-display state has not been realized to date. A method to realize a function that allows only partial lines of a liquid crystal display panel to be in a display state and the other to be in a non-display state has been proposed with Japanese Unexamined Patent Publication Nos. 6-95621 and 7-281632. Both of these two proposals disclose a method in which display duties are varied according to the case of a partial display and the case of a full-screen display so as to obtain driving voltages and bias ratios which are suitable to the individual duties.
The method proposed in Japanese Unexamined Patent Publication No. 6-95621 will be described below with reference to FIGS. 19 to 21. FIG. 19 is a block diagram showing an example of conventional liquid crystal display apparatuses. A block 51 represents a liquid crystal display panel (LCD panel) in which a substrate on which plural scanning electrodes are formed and a substrate on which plural signal electrodes are formed are arranged to oppose each other with a several-xcexcm gap, and a liquid crystal is enclosed in the gap. By the liquid crystal at cross sections of the scanning electrodes arranged in the line direction and the signal electrodes arranged in the column direction, pixels (dots) are to be formed in a matrix. A block 52 represents a scanning-electrode driving circuit (Y driver) that drives the scanning electrodes, and a block 53 represents a signal-electrode driving circuit (X driver) that drives the signal electrodes. Plural voltage levels necessary for driving the liquid crystal are formed in a driving-voltage forming circuit represented by a block 54 and are applied to the liquid crystal display panel 51 through the X driver 53 and the Y driver 52. A block 57 represents a scanning control circuit that controls the number of the scanning electrodes to be scanned. A block 55 represents a controller that supplies signals necessary for these circuits, FRM denotes a frame start signal, CLY denotes a scanning-signal transfer clock, CLX denotes a data transfer clock, Data denotes display data, LP denotes a data latch signal, and PD denotes a partial display control signal. A block 56 represents a power source for the circuits described above.
In this conventional example, a case in which the partial display appears on the left-half screen and on the upper-half screen is described; however, hereinbelow, a description will be given of the latter case in which lines for the upper-half screen are arranged in the display state and lines for the lower-half are arranged in the non-display state. The number of the scanning electrodes is assumed to be 400. The controller 55 turns the partial display control signal PD to an H level to allow the lower-half screen to be in the display state. When the partial display control signal PD is at an L level, all the scanning electrodes are scanned at a 1/400 duty, by which the full-screen is turned to the display state. When the partial display control signal PD is at the H level, only the scanning electrodes for the upper-half screen are scanned at a 1/200 duty, by which the upper-half screen is turned to the display state and the remaining lower-half screen is turned to the non-display state. Switching to the 1/200 duty is performed by switching to the duplicated cycle of the scanning-signal transfer clock CLY to reduce the number of clocks in one frame period. A scanning-stopping manner for the scanning electrodes for the lower-half screen in the partial display state is not described in detail. From the internal circuit diagram of the scanning control circuit block 57, however, the manner is considered to be such that as follows. That is, when the control signal PD is turned to the H level, data to be transferred from the 200th stage to the 201st stage of a shift register in the Y driver is fixed at the L level, resulting in that outputs of the 201st to the 400th from the Y driver, which are fed to the scanning electrodes of the 200th to the 400th, are maintained at a non-selection voltage level.
FIG. 20 shows an example of driving voltage waveforms indicating a horizontal line at every other scanning-electrode line in the partial display state of this conventional example. A represents waveforms of voltages applied to one pixel on the upper-half screen, and B represents waveforms of voltages applied to all the pixels on the lower-half screen. In the figure, bold lines in the waveforms A and B indicate scanning electrode driving waveforms, and thin lines indicate signal electrode driving waveforms.
A selection signal V0 (or V5) is sequentially applied to each line of the scanning electrodes for the upper-half screen in every selection period (one horizontal scanning period: 1 H), and a non-selection voltage V4 (or V1) is applied to other lines of the scanning electrodes. ON/OFF information regarding individual pixels on selected lines is sequentially applied to the signal electrodes synchronously with the horizontal scanning period. More particularly, in a period when application voltages for selected lines of the scanning electrodes are V0, V5 is applied to the signal electrodes of ON-pixels on selected lines and V3 is applied to the signal electrodes of OFF-pixels; in a period when application voltages are V5, V0 is applied to the signal electrodes of ON-pixels, and V2 is applied to the signal electrodes of OFF-pixels. The voltage applied to the liquid crystal for individual pixels is the differential voltage between the scanning voltage applied to the scanning electrode (the selection voltage and the non-selection voltage) and the signal voltage applied to the signal electrode (an ON-voltage and an OFF-voltage). On principle, when this differential voltage is higher, a pixel with a higher effective voltage is turned ON; while, when this differential voltage is lower, a pixel with a lower effective voltage is turned OFF.
On the other hand, as shown in B of FIG. 20, since no selection voltage is applied to the scanning electrode, effective voltages for pixels on the lower-half screen are reduced to be considerably lower than effective voltages applied to the OFF-pixels on the upper-half screen, causing the lower-half screen to be totally in the non-display state.
As shown with a liquid-crystal alternating-current driving signal M, FIG. 20 shows a case in which signal-polarity switching is carried out for a driving voltage in every selection period for 13 lines. In this way, in higher-duty driving for reduction of flickering, cross-talks, and other problems, signal-polarity switching must be carried out for the driving voltages in every selection period for some ten lines. Although the lower-half screen is in the non-display state, voltages applied to the scanning electrodes and the signal electrodes in the non-display region are varied, as shown in B of FIG. 20. In this case, a defect is caused such as that even after the screen turned to be in the partial display state, circuits such as drivers would still continue to operate, and charging and discharging of the liquid crystal would still continue; therefore, power consumption is not expectedly reduced.
For reference, for switching of the display duty, the simple-matrix liquid crystal display apparatus requires modification of setting the driving voltage. This will be described below with reference to FIG. 21, which is an internal circuit of the driving-voltage forming circuit block 54.
First, a description will be given of a construction and functions in FIG. 21. For driving a liquid crystal display panel of a duty higher than about 1/30 duty, voltages of six levels of V0 to V5 are necessary. The highest voltage to be applied to the liquid crystal is V0xe2x88x92V5, and the input power source voltage of V5 is used as it is for V0. By use of a variable resistor RV1 for contrast adjustment and a transistor Q1, the voltage V5 which will result in the suitable contrast is retrieved from an input power sources of 0 V and xe2x88x9224 V. Resistors R1 to R5 are used to divide the voltage V0xe2x88x92V5 for forming intermediate voltages, and operational amplifiers OP1 to OP4 are used to increase driving capacity of the intermediate voltages so as to output V1 to V4. Switches S2a and S2b are interlock switches, and either one of R3a and R3b is connected in series to R2xc2x7R4 in accordance with the level of the signal PD. Resistance values of R3a and R3b are differentiated so that V0 to V5 of a different voltage-division ratio can be formed according to the PD level.
Among V0 to V5 there is a relationship expressed by V0xe2x88x92V1=V1xe2x88x92V2 V3xe2x88x92V4=V4xe2x88x92V5, and a voltage division ratio (V0xe2x88x92V1)/(V0xe2x88x92V5) is called a bias ratio. Japanese Examined Patent Publication No. 57-57718 discloses that when the duty is 1/N, a preferable bias ratio is 1/(1+N). Accordingly, when resistance values of R3a and R3b are set for a 1/400 duty and a 1/200 duty, respectively, driving can be performed at preferable bias ratios.
To switch between duties, not only the bias-ratio switching is necessary, but the driving voltage (V0xe2x88x92V5) must also be modified. If the duty is switched from 1/400 to 1/200 with a fixed driving voltage, even when switching is performed so as to set preferable bias ratio, the display results in being of much lowered contrast. This is caused by the fact that time when selection voltages are added to the liquid crystal is duplicated to excessively increase effective voltages. In the conventional example, while necessity for the bias-ration switching and an implementation means therefor are disclosed in detail, necessity for the driving-voltage switching and an implementation means therefor are not disclosed in detail.
In particular, with a duty assumed to be 1/N, when N greater than  greater than 1, (V0xe2x88x92V5) must be adjusted substantially in proportion to N. For example, if a preferable (V0xe2x88x92V5) in case of 1/400 duty is 28 V, (V0xe2x88x92V5) must be adjusted to 28V/2≈20 V in case of 1/200 duty. This voltage adjustment is to be carried out by apparatus users by adjusting the contrast-adjustment variable resistor RV1 every time when switching is performed between the full-screen display state and upper-half screen display state. It is very inconvenient for apparatus users. Supplement of a driving-voltage automatic setting means is mandatory; however, it is not so easy as a bias-ratio switching means and the driving-voltage forming circuit will be much complicated. For reference, in the conventional publications, a description is given to the effect that since reduced driving voltages would be sufficient in a half-screen display, power consumption would be further reduced. However, since a large volume of the reduction voltage of 8 V is consumed to allow the contrast-adjustment transistor Q1 to generate heat, the power consumption is not reduced so much.
When the partial display is considerably smaller to cover some ten lines to twenty lines, duty-switching is carried out according to that display. By this, a preferable bias ratio, such as 1/3 and 1/4, can be obtained. In this case, voltage necessary for driving the liquid crystal is not any more the six levels, but will instead be five levels for the 1/4 bias and four levels for the 1/4 levels. When five levels of voltages are necessary, the resistance value at the side to be connected to either one of the resistors R3a and R3b may be set to 0 xcexa9. However, when four levels of voltages are necessary, the resisters R2 and R4 need to be 0 xcexa9, not the resisters R3a or R3b. A bias-ratio switching means and a driving-voltage switching means in a case as described above are disclosed in Japanese Unexamined Patent Publication No. 7-281632. However, a further description regarding a construction of the foregoing will be omitted here.
According to the aforementioned methods that have been proposed to date, basic functions for causing partial lines of a liquid crystal display panel to be in a display state and for causing other lines to be in a non-display state are realized, and power consumption can also be reduced to a certain extent. However, there still remains problems such as that a driving-voltage forming circuit will be very complicated, the number of lines that can be displayed is limited because of hardware, and reduction of power consumption is not yet sufficient.
Furthermore, the former Japanese Unexamined Patent Publication No. 6-95621 is relevant to a transmissive-type liquid crystal display panel, and the latter Japanese Unexamined Patent Publication No. 7-281632 states only about a partial-display method, in which display types are not disclosed. Whatever the transmissive type or reflective type, when higher contrast is considered important, liquid crystal display panels of a normally-black type have been conventionally used. The reasons are described below.
In case of a normally-white type, since regions among dots to which voltage is not applied are in white, white-display regions of a screen appear sufficiently in white, but black-display regions do not appear sufficiently in black. In contrast, In case of the normally-black type, since regions among dots to which voltage is not applied are in black, black-display regions of a screen appear sufficiently in black, but white-display regions do not appear sufficiently in white. Display can be in higher contrast in the case the black-display region appear sufficiently in black than in the case where the white-display regions appear sufficiently in white. For these reasons, use of the normally-black type liquid crystal display panel provides higher contrast.
For reference, the normally-black type is a mode in which a black-display is provided when the effective voltage applied to the liquid crystal is an OFF-voltage which is lower than a threshold of the liquid crystal, and a white-display is provided when the application voltage is increased and an ON-voltage higher than the threshold of the liquid crystal is applied to the liquid crystal. On the other hand, the normally-white type is a mode in which a white-display is provided when the effective voltage applied to the liquid crystal is an OFF-voltage which is lower than a threshold of the liquid crystal, and a black-display is provided when the effective voltage is increased and an ON-voltage higher than the threshold of the liquid crystal is applied to the liquid crystal. For example, when a substantially 90-degree twisted nematic type liquid crystal is used, the liquid crystal display panel has a paired polarizers on two side faces of the liquid crystal display panel; when transmissive axes of the paired polarizers are arranged substantially parallel, the normally-black type is made; when the transmissive axes of the paired polarizers are arranged substantially perpendicular, the normally-white type is made.
FIG. 18 is a drawing illustrating a partial display state in the case when the normally-black type liquid crystal display panel 107 is used. Since the OFF-voltage or the effective voltage lower than the OFF-voltage is applied to the liquid crystal in the non-display region, as shown in the figure, the non-display region provides the black-display. On the other hand, in the reflective type liquid crystal display panel, characters must be displayed in black and the background must be displayed in white so that incident light is reflected to make a bright and easy-to-view display. However, with the normally-black type liquid crystal display panel, while the background of the display region appears in white, the non-display region appears in black. This partial display state is incompatible. Furthermore, with display dots positioned at the border between the display region and the non-display region on the display screen, black-display dots forming characters in the display region and black-display dots in the non-display region become adjacent dots, causing a chained-character display when it is viewed. This gives rise to a problem in that the characters displayed on the dots on the border between the display region and the non-display region are difficult to be identified. For making the non-display region a white display so as not to being incompatible, the ON-voltage needs to be applied to the liquid crystal in the non-display region. On principle, however, such a non-display region cannot be referred to as a real non-display region. If the non-display region is arranged to be the white-display, problems arise such as those described as below. Power consumption by circuits necessary for realizing such an arrangement cannot be reduced. In addition, in a case where liquid crystal molecules are arrayed in the horizontal direction in an OFF-state and are allowed to rise in an ON-state as a nematic liquid crystal, permittivity of liquid crystals in the ON-state is two to three times higher than that in the OFF-state. In this condition, when the liquid crystal is driven to an ON-state so as to display the non-display region in white, charging and discharging current due to AC driving of a liquid crystal layer is increased; in which case, as compared to the case in the full-screen display state, the power consumption in the full-screen display state is not reduced so much, or conversely, is increased.
As described above, when the normally-black type liquid crystal display panel is simply adopted for improvement of contrast, the resulting display is incompatible, because the non-display region is the black-display in the partial display state. Furthermore, if the non-display region is arranged to be the white-display which is not incompatible, it is difficult to refer to such an arrangement as realization of a partial display function when it is viewed on principle, and in addition, an object of power consumption cannot be achieved.
To these ends, an object of the present invention is to solve the problems with the conventional art and is to provide an electrooptical apparatus allowing great reduction of power consumption. It is another object to provide an electrooptical apparatus not allowing a driving-voltage forming circuit to be complicated for the partial display function, and allowing the size and the position of the partial display to set by software so as to improve general usability thereof.
It is another object to provide an liquid crystal display apparatus realizing a display not producing an incompatible result and allowing great reduction of power consumption in a partial display state when it is used as an electrooptical apparatus.
It is another object to provide a construction of a driving circuit suitable for driving the electrooptical apparatus of the present invention.
It is another object to provide an electronic equipment utilizing an electrooptical apparatus or a liquid crystal display apparatus as a display apparatus, which includes the partial display function, to allow reduction of power consumption.
The present invention provides a driving method for an electrooptical apparatus, in which a plurality of scanning electrodes and a plurality of signal electrodes are arranged to cross with each other and comprises a function partially causing a display screen to be a display region, characterized in that selection voltages are applied in a selection period and non-selection voltages are applied in a non-selection period to the scanning electrodes in the display region; and in a period other than the selection period, application voltages for all the scanning electrodes in the display region are fixed, and application voltages for all the signal electrodes are fixed at least in a predetermined period; by which the display screen is shifted to the partial display state. According to the present invention, in the partial display, in which only a partial region is in the display region state, potentials of all the scanning electrodes and all the signal electrodes are fixed at least in the predetermined period; therefore, periods in which charging and discharging are not caused with components, such as liquid crystal layers of electrooptical materials, electrodes, and driving circuits, to reduce power consumption by electrical quantity saved as above.
Furthermore, in the driving method for the electrooptical apparatus of the present invention, it is preferable that voltages for the scanning electrodes in the period when the application voltages for all the scanning electrodes are fixed are to be the non-selection voltages. In the case of the partial display, since the voltages of the scanning electrodes which are fixed are the non-selection voltages, the driving circuits can be formed of simple circuits.
Furthermore, in the driving method for the electrooptical apparatus of the present invention, it is preferable that the non-selection voltages are one level. In a non-display region access period, since the non-selection voltages can be fixed at one level, no voltage variation occurs; therefore, reduced power consumption can be implemented.
Furthermore, in the driving method for the electrooptical apparatus of the present invention, it is preferable that a forming circuit for driving voltages to be applied to the scanning electrodes and the signal electrodes stops its operation in the period when the individual application voltages for all the scanning electrodes and all the signal electrodes are fixed. More particularly, it is preferable that the driving-voltage forming circuit includes a charge-pump circuit that switches among a plurality of capacitor connections according to clocks to generate boosted voltages and dropped voltages, and operation of the charge-pump circuit is stopped in the period when the individual application voltages for all the scanning electrodes and all the signal electrodes are fixed. By such an arrangement, in the period of the partial display state, power consumption in the driving-voltage forming circuit can be reduced. When the charge-pump circuit is used for increasing or dropped voltages, in a manner such as that the timing clocks that switch among capacitors, wasted power consumption can be reduced.
In connection with the invention described above, one driving method for a simple-matrix liquid crystal display apparatus in which non-selection voltages are only one level is that called an MLS (multi-line selection) driving method that selects multilines of scanning electrodes simultaneously, and another is that called an SA (smart-addressing) driving method that selects scanning electrodes one by one. A proposal has been made in International Patent Application Laid-Open No. WO96/21880 stating that by combining the aforementioned methods and a driving-voltage forming circuit formed of a charge-pump circuit, power consumption by a liquid crystal display apparatus can be greatly reduced. The present invention aims for further reduction of power consumption based on the above-referenced WO96/21880 and by developing the concept so as to be applicable to a partial display function.
The period other than the selection period in the scanning electrodes in the display region refers to a period other than a period when the selection voltages are applied to display lines (hereinbelow, this period is referred to as non-display line access period), at which time potentials of all the scanning electrodes and all the signal electrodes are fixed so that power consumption in the driving circuits can be greatly reduced and the electrooptical apparatus can be a less-power-consumption type. Furthermore, stopping operations of the charge-pump circuit of the driving-voltage forming circuit in the period allows charging and discharging due to the capacitors therein to be avoided, further reducing the power consumption. In the period, the capacitors do not discharge electricity because power consumption in the driving circuits is very low, so that even when the charge-pump circuit stops its operations, variations of the driving voltages are within a level giving no rise to a problem.
Furthermore, in the driving method for the electrooptical apparatus of the present invention, it is preferable that the driving method includes a first display mode causing the full portion of the display screen to be in a display state and a second display mode causing one partial region to be in a display state of the display screen and the other to be a non-display state, and the length of the period when the selection voltages are applied to the individual scanning electrodes in the display region is not changed for the first display mode and the second display mode. According to this invention, times in which the selection voltages are applied to the scanning electrodes in the display regions in the case of the full-screen display and in the case of the partial display are the same; that is, duties are the same. Therefore, no modification of bias ratios and the driving voltages at the time of partial display is necessary, and the driving circuits, the driving-voltage forming circuit, and the like do not need to be complicated.
Furthermore, in the driving method for the electrooptical apparatus according to the present invention described above, it is preferable that potentials are set for the signal electrodes in the period other than the selection period for the scanning electrodes in the display region so that effective voltages to be applied to a liquid crystal for pixels in the display region in the display state are the same in the first display mode and the second display mode. According to this invention, since potentials of the signal electrodes are set such that the effective voltages applied to the liquid crystal of an electrooptical material become the same in two cases of the full-screen display and the partial display, an arrangement can be made such that contrast in the display regions remains unchanged.
Furthermore, in the driving method for the electrooptical apparatus according to the present invention described above, it is preferable that potentials to be applied to the signal electrodes in the period other than the selection period for the scanning electrodes in the display region are set so as to be the same as the application voltages for the signal electrodes in the case of an ON-display or an OFF-display in the first display mode. Since the signal voltages in the full-screen display are used as they are, the driving circuits and driving control can be simplified.
Furthermore, in the driving method for the electrooptical apparatus according to the present invention described above, it is preferable that the method is driven so that the plurality of scanning electrodes are simultaneously selected in the unit of a predetermined number and are sequentially selected on the basis of a predetermined number of units, and the application voltages for the signal electrodes in the case of the ON-display or the OFF-display in the second display mode are set so as to be the same as the application voltages for the signal electrodes in the case of full-screen ON-display or full-screen OFF-display in the first display mode. In such an arrangement, in the MLS driving method, the effective voltages applied to the liquid crystal in the display regions in the case of the full-screen display and in the case of the partial display can be arranged to be the same, and concurrently, image quality in the case of the partial display can be maintained to be sufficiently high. Increase in circuit size can also be minimized.
Furthermore, in the driving method for the electrooptical apparatus according to the present invention described above, it is preferable that the potentials to be applied to the signal electrodes in the period other than the selection period for the scanning electrodes in the display region are set by alternately switching, on the basis of the predetermined period for one-screen scanning, between the application potential when the ON-display is performed and the application potential when the OFF-display is performed in the full screen display state. Furthermore, in the driving method for an electrooptical apparatus according to the present invention described above, it is preferable that in the period other than the selection period for the scanning electrodes in the display region in the second display mode, polarity of the voltage difference between the scanning electrodes and the signal electrodes is inverted in every frame. In such an arrangement, power consumption in the non-display access period can be greatly reduced. When the number of the partial-display lines is small (for example, not greater than about 60 lines), even when liquid-crystal driving voltages for pixels on non-display lines are fixed, image quality of the entire screen is not lowered.
Furthermore, the present invention provides the driving method for the electrooptical apparatus, in which a plurality of scanning electrodes and a plurality of signal electrodes are arranged to cross with each other and comprises a function partially causing a display screen to be a display region, characterized in that selection voltages are applied in a selection period and non-selection voltages are applied in a non-selection period to the scanning electrodes in the display region; and the selection voltages are not applied, but the non-selection voltages are applied to the scanning electrodes in a region other than the display region of the display screen and the application voltages for all the signal electrodes are fixed at least in a period longer than a same-polarity driving period in polarity-inversion driving state and a full-screen display state; by which the display screen is changed to the partial display state. According to the present invention, in the partial display, in which only a partial region is the display region, potentials of all the scanning electrodes and all the signal electrodes are fixed at least in the predetermined period; therefore, periods in which charging and discharging are not caused with components, such as liquid crystal layers of electrooptical materials and driving circuits of electrodes, to reduce power consumption by electrical quantity saved as above.
Furthermore, in the driving method for the electrooptical apparatus according to the present invention described above, it is preferable that the application voltages for the signal electrodes are alternately switched between a potential when an ON-display is performed and a potential when an OFF-display is performed in the full-screen display state on the basis of a period which is at least longer than the same-polarity driving period in the polarity inversion driving state and the full-screen display state. Even in the non-display line access period, since polarity inversion is performed on a cycle basis for the driving voltages, such problems as direct-current application and crosstalk can be avoided.
The driving method for the electrooptical apparatus described above can be realized by use of a simple-matrix liquid crystal display apparatus or an active-matrix liquid crystal display apparatus.
Furthermore, the present invention provides an electrooptical apparatus according to the present invention is characterized to be driven by the driving method described above. By this arrangement, the electrooptical apparatus of a less-power-consumption type can be provided.
Furthermore, the present invention provides an electrooptical apparatus including a plurality of scanning electrodes and a plurality of signal electrodes which are arranged to cross with each other and a function partially causing a display screen to be a display region, characterized by comprising a scanning-electrode driving circuit for applying selection voltages to the plurality of scanning electrodes in a selection period and applying non-selection voltages to the plurality of scanning electrodes in a non-selection period; a signal-electrode driving circuit for applying signal voltages according to display data to the plurality of signal electrodes; setting means for setting positional information regarding a partial display region in the display screen; and control means for outputting a partial display control signal that controls the scanning-electrode driving circuit and the signal-electrode driving circuit based on the positional information set by the setting means; wherein the scanning-electrode driving circuit and the signal-electrode driving circuit driving the scanning electrodes and the signal electrodes according to the partial display control signal, so that the scanning electrodes and the signal electrodes in the display region in the display screen are driven so as to cause display according to the display data and the non-selection voltages are applied continuously to the scanning electrodes in the non-selection region in the display screen; by which a non-display state is caused. According to this present invention, no modification with respect to items such as duty, bias ratios, liquid-crystal driving voltages in hardware circuits for the partial display is required, the number of display lines or non-display lines and position can be set to a resister of the control circuit. With such an arrangement, an electrooptical apparatus with high general usability in which the number of partial display lines and the position can be set in software mode.
Furthermore, the electrooptical apparatus described above can be realized by use of a simple-matrix liquid crystal display apparatus or an active-matrix liquid crystal display apparatus.
Furthermore, the present invention provides a driving circuit for an electrooptical apparatus, in which a plurality of scanning electrodes and a plurality of signal electrodes are arranged to cross with each other and comprises a function partially causing a display screen to be a display region, characterized by comprising first driving means applying voltages to the plurality of scanning electrodes; and second driving means comprising a storing circuit to store display data and applying voltages selected according to the display data read from the storing circuit to the plurality of signal electrodes; the first driving means having a function that applies selection voltages in a selection period and applies non-selection voltages in a non-selection period to the scanning electrodes in the display region, and applies only the non-selection voltages to the scanning electrodes in other region of the display screen; and the second driving means having a function that reads the display data from the storing circuit in a period corresponding to the selection period for the scanning electrodes in the display region and fixed address for reading the display data from the storing circuit in other periods. According to the present invention, by stopping readout operations for the display data from the storing means included in a signal-electrode driving circuit, consumption current in the signal-electrode driving circuit in the non-display access period can be substantially reduced to about zero. At this time, when readout display information is fixed at 0 or 1, an output from the signal-electrode driving circuit can be fixed to the same voltage as that in the case of the full-screen ON-display or the full-screen OFF-display.
Furthermore, in the electrooptical apparatus according to the present invention described above, it is preferable that a shift register in the first driving means stops its shift operations in a period other than the selection period of the scanning electrodes in the display region. According to this invention, in the period, since the scanning-electrode driving circuit does not output the selection voltages, the shift register does not need to operate. When operations of the shift register is stopped by stopping a shift-clock, power consumption in the scanning-electrode driving circuit in this period can be substantially reduced to zero.
Furthermore, the present invention provides the driving circuit for an electrooptical apparatus, in which a plurality of scanning electrodes and a plurality of signal electrodes are arranged to cross with each other and comprises a function partially causing a display screen to be a display region, characterized by comprising a scanning-electrode driving circuit for applying selection voltages sequentially to the plurality of scanning electrodes according to shift operations by a shift register, the scanning-electrode driving circuit applying selection voltages in a selection period to the scanning electrodes in the display region of the display screen according to shift operations by the shift register and applying only the non-selection voltages to the scanning electrodes in other region of the display screen by stopping the shift operations by the shift register on a way when partially causing the display screen to be the display region, and the scanning-electrode driving circuit comprising an initial setting means to reset the shift register to an initial state when changing a state in which the display screen is caused to be in the partial display state to in a full-screen state. According to this invention, at the time of transition from the partial display state to the full-screen display state, scanning is not started from an undefined position and can be started from the first line of the scanning electrodes.
Furthermore, the present invention provides the electrooptical apparatus characterized by comprising the driving circuit and scanning electrodes and signal electrodes to be driven by the driving circuit. By this arrangement, a partial display can be implemented, and the electrooptical apparatus of a less-power-consumption type can be provided.
Furthermore, the present invention provides an electrooptical apparatus in which a plurality of scanning electrodes and a plurality of signal electrodes are arranged to cross with each other and comprises a function partially causing a display screen to be a display region, characterized by comprising first driving means applying voltages to the plurality of scanning electrodes; and second driving means comprising a storing circuit to store display data and applying voltages selected according to the display data read from the storing circuit to the plurality of signal electrodes; the first driving means having a function that applies selection voltages in a selection period and applies non-selection voltages in a non-selection period to the scanning electrodes in the display region of the display screen, and applies only the non-selection voltages to the scanning electrodes in other region of the display screen; and the second driving means having a function that applies voltages to the plurality of signal electrodes in a selection period of the scanning electrodes of the display region on the basis of display data read from the storing circuit and applies voltages to the plurality of signal electrodes in the other period on the basis of the same display data. According to the present invention, by stopping readout operations for the display data from the storing means included in a signal-electrode driving circuit, consumption current in the signal-electrode driving circuit in the non-display access period can be substantially reduced to about zero.
Furthermore, in the electrooptical apparatus according to the present invention described above, it is preferable that the second driving means alternately changes, in a period other than the selection period for scanning electrodes in the display region, the application voltages for the signal electrodes between a potential when an ON-display is performed and a potential when an OFF-display is performed in a full-screen display state, on the basis of a period which is at least longer than a same-polarity driving period in a polarity inversion driving in the full-screen display state. Even in the non-display line access period, since polarity inversion is performed on a cycle basis for the driving voltages, such problems as direct-current application and crosstalk can be avoided.
Furthermore, in the electrooptical apparatus according to the present invention described above, it is preferable that it comprises a driving-voltage forming circuit for forming voltages applied to the scanning electrodes or the signal electrodes to supply them to the driving means, the driving-voltage forming circuit including a contrast adjustment circuit for adjusting the application voltage, and characterized by stopping operations of the contrast adjustment circuit in a period other than the period of selection of the scanning electrodes in the display region. In the electrooptical apparatus of this invention, power consumption in the driving circuits in the non-display line access period is very small. Therefore, as long as the driving voltages are retained in the capacitors, even when the contrast adjustment circuit is stopped, variations of the driving voltages are very small, so that no rise is given to a substantial problem. Power consumption of the driving circuit can be further reduced by stopping the contrast adjustment circuit.
Furthermore, the present invention provides a driving method for a liquid crystal display apparatus which is a reflective type or a transflective type allowing a partial display state by enabling a partial region in a full screen of a liquid crystal display panel to be turned to a display state and the other to be turned to a non-display state, characterized in that the liquid crystal display panel is a normally-white type and effective voltages equal to or lower than the OFF-voltage are applied to a liquid crystal in the non-display region in the partial display state. By use of the normally-white type, the non-display region appears in white in the partial display state; therefore, display which is not incompatible can be provided. Furthermore, as a circuit means that applies effective voltages equal to or lower than the OFF-voltage to the liquid crystal in the non-display region, a simple means that use lower power consumption can be used; furthermore since permittivity of the liquid crystal in the non-display region is small, charging and discharging current due to AC driving of the liquid crystal is reduced; in which case, as compared to the case in the full-screen display state, the power consumption in the entire display apparatus can be greatly reduced.
Furthermore, in the driving method for the liquid crystal display apparatus according to the present invention described above, it is preferable that the liquid crystal display panel is a simple-matrix liquid crystal panel in which only non-selection voltages are applied to scanning electrodes in the non-display region in the partial display state. Furthermore, the liquid crystal display panel is a simple-matrix liquid crystal panel; and it is preferable that only voltages that turn to be the OFF-display are applied to the signal electrodes in the partial display state.
Furthermore, in the driving method for the liquid crystal display apparatus according to the present invention described above, it is preferable that the liquid crystal display panel is a simple-matrix liquid crystal panel in which only voltages equal to or lower than OFF-voltages are applied to a liquid crystal for pixels in the non-display region at least in the first frame changing to the partial display state, and only non-selection voltages are applied to scanning electrodes in the non-display region in and from the following frame. Furthermore, it is preferable that the liquid crystal display panel is an active-matrix type liquid crystal display panel, in which voltages equal to or lower than the OFF-voltage are applied to the liquid crystal for pixels in the non-display region at least in the first frame changing to the partial display state, and only voltages equal to or lower than the OFF-voltage are applied to the signal electrodes in an access period for the non-display region in and from the following frame.
By this arrangement, partial display regions are arranged in the line direction and in the column direction on the display screen, and other region can be arranged to be a non-display region. Furthermore, since the liquid crystal display panel is the normally-white type, the non-display region appears in white in the partial display state; therefore, a compatible display can be provided. Furthermore, since high voltages are not applied to pixels in the non-display region, less power consumption can be realized.
Furthermore, the present invention provides the liquid crystal display apparatus characterized to be driven by the driving method for the liquid crystal display apparatus and provides a liquid crystal display apparatus of less-power-consumption type and less incompatible even in the partial display state.
Furthermore, the present invention provides an electronic equipment utilizing the electrooptical apparatus or the liquid crystal display apparatus as a display apparatus. Particularly, when the electronic equipment uses battery as a power source, battery service life can be extended.